Patched Arel v2.0.6 to support MSSQL SQL queries. Based on work of Ja…

…mes Abley (https://github.com/jabley/arel).

lib/arel/nodes.rb

@@ -24,6 +24,8 @@
 require 'arel/nodes/count'
 require 'arel/nodes/values'
 require 'arel/nodes/offset'
+require 'arel/nodes/limit'
+require 'arel/nodes/top'
 require 'arel/nodes/sum'
 require 'arel/nodes/exists'
 require 'arel/nodes/max'

lib/arel/nodes/limit.rb

@@ -0,0 +1,7 @@
+module Arel
+  module Nodes
+    class Limit < Arel::Nodes::Unary
+    end
+  end
+end
+

lib/arel/nodes/select_core.rb

@@ -1,10 +1,11 @@
 module Arel
   module Nodes
     class SelectCore < Arel::Nodes::Node
-      attr_accessor :froms, :projections, :wheres, :groups
+      attr_accessor :top, :froms, :projections, :wheres, :groups
       attr_accessor :having
 
       def initialize
+        @top         = nil
         @froms       = nil
         @projections = []
         @wheres      = []

lib/arel/nodes/top.rb

@@ -0,0 +1,6 @@
+module Arel
+  module Nodes
+    class Top < Arel::Nodes::Unary
+    end
+  end
+end

lib/arel/select_manager.rb

@@ -10,7 +10,7 @@ def initialize engine, table = nil
     end
 
     def taken
-      @ast.limit
+      @ast.limit && @ast.limit.expr
     end
 
     def constraints
@@ -131,7 +131,8 @@ def where_sql
     end
 
     def take limit
-      @ast.limit = limit
+      @ast.limit = Nodes::Limit.new(limit)
+      @ctx.top   = Nodes::Top.new(limit)
       self
     end
 

lib/arel/visitors.rb

@@ -4,6 +4,7 @@
 require 'arel/visitors/sqlite'
 require 'arel/visitors/postgresql'
 require 'arel/visitors/mysql'
+require 'arel/visitors/mssql'
 require 'arel/visitors/oracle'
 require 'arel/visitors/join_sql'
 require 'arel/visitors/where_sql'
@@ -16,6 +17,8 @@ module Visitors
       'postgresql'      => Arel::Visitors::PostgreSQL,
       'mysql'           => Arel::Visitors::MySQL,
       'mysql2'          => Arel::Visitors::MySQL,
+      'mssql'           => Arel::Visitors::MSSQL,
+      'sqlserver'       => Arel::Visitors::MSSQL,
       'oracle_enhanced' => Arel::Visitors::Oracle,
       'sqlite'          => Arel::Visitors::SQLite,
       'sqlite3'         => Arel::Visitors::SQLite,

lib/arel/visitors/mssql.rb

@@ -0,0 +1,16 @@
+module Arel
+  module Visitors
+    class MSSQL < Arel::Visitors::ToSql
+      private
+
+      def visit_Arel_Nodes_Limit o
+        ""
+      end
+
+      def visit_Arel_Nodes_Top o
+        "TOP #{visit o.expr}"
+      end
+
+    end
+  end
+end

lib/arel/visitors/mysql.rb

@@ -10,7 +10,7 @@ def visit_Arel_Nodes_Lock o
       # :'(
       # http://dev.mysql.com/doc/refman/5.0/en/select.html#id3482214
       def visit_Arel_Nodes_SelectStatement o
-        o.limit = 18446744073709551615 if o.offset && !o.limit
+        o.limit = Arel::Nodes::Limit.new(18446744073709551615) if o.offset && !o.limit
         super
       end
 

lib/arel/visitors/sqlite.rb

@@ -3,7 +3,7 @@ module Visitors
     class SQLite < Arel::Visitors::ToSql
       private
       def visit_Arel_Nodes_SelectStatement o
-        o.limit = -1 if o.offset && !o.limit
+        o.limit = Arel::Nodes::Limit.new(-1) if o.offset && !o.limit
         super
       end
     end

lib/arel/visitors/to_sql.rb

@@ -76,15 +76,17 @@ def visit_Arel_Nodes_SelectStatement o
         [
           o.cores.map { |x| visit_Arel_Nodes_SelectCore x }.join,
           ("ORDER BY #{o.orders.map { |x| visit x }.join(', ')}" unless o.orders.empty?),
-          ("LIMIT #{visit o.limit}" if o.limit),
+          (visit(o.limit) if o.limit),
           (visit(o.offset) if o.offset),
           (visit(o.lock) if o.lock),
         ].compact.join ' '
       end
 
       def visit_Arel_Nodes_SelectCore o
         [
-          "SELECT #{o.projections.map { |x| visit x }.join ', '}",
+          "SELECT",
+          (visit(o.top) if o.top),
+          "#{o.projections.map { |x| visit x }.join ', '}",
           ("FROM #{visit o.froms}" if o.froms),
           ("WHERE #{o.wheres.map { |x| visit x }.join ' AND ' }" unless o.wheres.empty?),
           ("GROUP BY #{o.groups.map { |x| visit x }.join ', ' }" unless o.groups.empty?),
@@ -100,6 +102,15 @@ def visit_Arel_Nodes_Offset o
         "OFFSET #{visit o.expr}"
       end
 
+      def visit_Arel_Nodes_Limit o
+        "LIMIT #{visit o.expr}"
+      end
+
+      # FIXME: this does nothing on most databases, but does on MSSQL
+      def visit_Arel_Nodes_Top o
+        ""
+      end
+
       # FIXME: this does nothing on SQLLite3, but should do things on other
       # databases.
       def visit_Arel_Nodes_Lock o

test/visitors/test_mssql.rb

@@ -0,0 +1,18 @@
+require 'helper'
+
+module Arel
+  module Visitors
+    describe 'the mssql visitor' do
+      before do
+        @visitor = MSSQL.new Table.engine
+      end
+
+      it 'uses TOP to limit results' do
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.last.top = Nodes::Top.new(1)
+        sql = @visitor.accept(stmt)
+        sql.must_be_like "SELECT TOP 1"
+      end
+    end
+  end
+end

test/visitors/test_to_sql.rb

@@ -32,7 +32,7 @@ module Visitors
 
       it "should escape LIMIT" do
         sc = Arel::Nodes::SelectStatement.new
-        sc.limit = "omg"
+        sc.limit = Arel::Nodes::Limit.new("omg")
         assert_match(/LIMIT 'omg'/, @visitor.accept(sc))
       end